Patent Watch

November 21, 2011

Convert unwanted p-ethyltoluene to desirable hydrocarbons. The methylation of toluene to p-xylene has been investigated for many years. Toluene has relatively little demand as a feedstock for petrochemicals manufacture, whereas p-xylene is in high demand as the feedstock for making terephthalic acid for polyester production. S. H. Brown and J. S. Buchanan disclose a twist to this tactic. They found that phosphorus-stabilized zeolite ZSM-5 allows methanol to react with inexpensive p-ethyltoluene; the catalyst not only facilitates the methylation of the aromatic ring, but it also forms the commercially valuable olefins ethylene and propylene.

The inventors used phosphorous-stabilized ZSM-5 to catalyze the reaction of a 4:1 w/w MeOH–p-ethyltoluene feedstock at 390 °C, 101.3 kPa absolute pressure, and a flow rate equivalent to a 0.7 h–1 weight hourly space velocity. p-Ethyltoluene conversion was 25%. The yield of major products is shown in the table.

Product

Yield, wt%

Ethylene

9.5

Propylene

7

Butenes

3

C5+ nonaromatics

2.5

p-Xylene

2.5

Me2O + MeOH

29

H2O

29

The MeOH conversion to hydrocarbon products was 67 wt%. Unreacted p-ethyltoluene amounted to 15 wt% of the reaction mixture.

The ability to convert little-used materials such as p-ethyltoluene to commercially important petrochemical building blocks may improve the overall economics of steam cracking in a chemical plant and catalytic reforming in an oil refinery. (ExxonMobil Chemical Patents [Houston]. US Patent 8,048,388, Nov. 1, 2011; Jeffrey S. Plotkin)